package com.lb.stream;

import lombok.Data;

import java.math.BigDecimal;
import java.util.*;
import java.util.stream.Collectors;

import static java.util.Comparator.comparing;
import static java.util.stream.Collectors.collectingAndThen;
import static java.util.stream.Collectors.toCollection;

/**
 * @Author: zhangjun
 * @Date: 2020/5/19 16:10
 * @Description:
 */
public class ListTest {
    public static void main(String[] args) {
        List<Apple> appleList = new ArrayList<>();//存放apple对象集合

        Apple apple1 = new Apple(1,"苹果1",new BigDecimal("3.25"),10);
        Apple apple12 = new Apple(1,"苹果2",new BigDecimal("1.35"),20);
        Apple apple2 = new Apple(2,"香蕉",new BigDecimal("2.89"),30);
        Apple apple3 = new Apple(3,"香蕉",new BigDecimal("9.99"),40);

        appleList.add(apple1);
        appleList.add(apple12);
        appleList.add(apple2);
        appleList.add(apple3);

        /**
         * 1、分组
         * List里面的对象元素，以某个属性来分组，例如，以id分组，将id相同的放在一起：
         */
        //List 以ID分组 Map<Integer,List<Apple>>
        Map<Integer, List<Apple>> groupBy = appleList.stream().collect(Collectors.groupingBy(Apple::getId));
        System.out.println(groupBy);

        /**
         * 2、List转Map
         * List -> Map
         * 需要注意的是：
         * toMap 如果集合对象有重复的key，会报错Duplicate key ....
         * apple1,apple12的id都为1。
         * 可以用 (k1,k2)->k1 来设置，如果有重复的key,则保留key1,舍弃key2
         */
        Map<Integer, Apple> appleMap = appleList.stream().collect(Collectors.toMap(Apple::getId, a -> a,(k1,k2)->k1));
        System.out.println(appleMap);

        /**
         * 3、过滤Filter
         * 从集合中过滤出来符合条件的元素
         */
        List<Apple> filterList = appleList.stream().filter(a -> a.getName().equals("香蕉")).collect(Collectors.toList());
        filterList.forEach(System.out::println);

        /**
         * 4.求和
         * 将集合中的数据按照某个属性求和:
         */
        BigDecimal totalMoney = appleList.stream().map(Apple::getMoney).reduce(BigDecimal.ZERO, BigDecimal::add);
        System.err.println("totalMoney:"+totalMoney);

        // 根据id降序排列，并去除name相同的元素
        List<Apple> unique = appleList.stream().sorted(Comparator.comparing(Apple::getId).reversed())
                .collect(collectingAndThen(
                        toCollection(() -> new TreeSet<>(comparing(Apple::getName))), ArrayList::new)
        );
        System.out.println("=======>" + unique);
    }
}

@Data
class Apple {
    private Integer id;
    private String name;
    private BigDecimal money;
    private Integer num;
    public Apple(Integer id, String name, BigDecimal money, Integer num) {
        this.id = id;
        this.name = name;
        this.money = money;
        this.num = num;
    }
}